The Fuel System

In an aircraft, many systems work in synergy, but in this blog post, I will write about issues arising in the fuel system. The fuel system is designed to deliver an uninterrupted supply of clean fuel from the fuel tanks to the engine, in a continuous flow. It must be available to the engine under all situations of engine power, altitude, attitude, and throughout all allowed flying maneuvers. There are two kinds of fuel systems: the gravity-feed system, which utilizes the force of gravity to get fuel to the engines; and the fuel-pump system, in which aircraft have two fuel pumps. In this system, the main pump system is powered by an engine, with an electrically powered auxiliary pump available for use during engine startup and in the event that the engine pump fails.

The fuel system is composed of different parts, including the fuel primer, fuel tanks, fuel selectors, fuel gauges, fuel strainers, sumps, and drains. Due to all of these components, there are many issues that could arise. Engines are difficult to start in cold weather, therefore the fuel primer comes in handy since there isn't enough heat sufficient to vaporize the fuel in the carburetor. When not in use, it is critical to secure the primer. If the knob is allowed to move during flight, it might vibrate out of place, resulting in an abnormally rich fuel-air mixture. To avoid this problem (overpriming), pilots must study the aircraft's priming guidelines. Another issue that can arise in the fuel system is in the fuel tanks. In order to avoid issues with fuel tanks, pilots must preform a preflight check including sampling the fuel from the strainers to see there is no water, settlements, or contaminants, as well as correct octane (100VLL A VGAS).

In order to prevent issues with fuel gauges, we must check any result that isn't "empty" should be double-checked. Pilots should not rely on the fuel quantity gauges' accuracy alone. During the preflight inspection, pilots must visually inspect the fuel level in each tank and compare it to the fuel quantity indication. There's great importance in being through on preflight fuel checks because there's plenty of evidence that debris (metal filings, rivets, sealant particles, etc) sneaks into fuel systems, clogging screens and disrupting normal fuel flow in new installations and, especially, following repair and maintenance.

It is also extremely important to drain the fuel strainer before each flight as well as check for water and contaminants. If in very cold environments the water in the strainer freezes, it could cause a clog in the fuel lines, leading to engine failure. In addition, in hot weather, it might pour into the carburetor and cause the engine to shut down. Finally, we must also be careful about fuel system icing. This might happen as a result of mechanical agitation of free water or temperature change of dissolved water. In order to prevent issues, we can use anti-icing additives that have been approved. However, we must keep in mind that anti-icing compounds are not a substitute for carburetor heat.

To conclude, by performing regular maintenance, completing preflight checks, and complying with the airworthiness requirements, we are able to prevent issues in this system.



 

 

Resources:

Bingelis, T. (1994). Avoiding Fuel Related Problems. EAA. Retrieved January 27, 2022, from https://www.eaa.org/eaa/aircraft-building/builderresources/while-youre-building/building-articles/fuel-systems/avoiding-fuel-related-problems

 

Federal Aviation Administration (FAA). (2016). Pilot’s Handbook of Aeronautical Knowledge  (PHAK). Retrieved  https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/


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